Electrical contact elements



May 21, 1957 K. c. UNDERWOOD E.TAL 2,793,273

ELECTRICAL CONTACT ELEMENTS Filed April 20, 1954 IN VEN TORS KENNETH C. (IA/05R W000 AND BY/L/OBAATM L/OH/VSO/V A TTOE/VEY ELECTRICAL CONTACT ELEMENTS Kenneth C. Underwood, Glen Ridge, and Hobart M. Johnson, Plainfield, N. J., assignors to Baker & Co., Inc, Newark, N. J., a corporation of New Jersey Application April 20, 1954, Serial No. 424,352

4 Claims. (Cl. 200-166) The present invention relates to electrical contact elements suitable for use in making and breaking electrical current and is concerned in particular with mated precious metal contacts.

Electrical contacts of silver have found the widest general use, as silver has excellent electric current carrying capacity and is relatively cheap compared with other contact materials, such as platinum and the like. However, silver contacts, including fine silver contacts and silver alloy contacts suffer from the disadvantages of welding or sticking, coning and craten'ng as well as metal transfer from one contact to the other, and such disadvantages are magnified when heavy electric currents are employed, thus limiting the field of usefulness of such contact both with respect to the life and the number of possible uses and applications thereof. Attempts have, therefore, been made to improve silver and the like contacts, primarily by incorporation of other metals in one form or another, with a view to modifying the properties of such contacts and decreasing such shortcomings. Some notable success has been achieved in one direction or another but further improvements are desirable in order to expand the usefulness of electrical contacts especially in the field of circuit breakers and voltage regulators in order to increase the useful life of electrical contact elements.

It is an object of the present invention to improve the operation of precious metal contacts. It is another object of the invention to provide electrical contacts of precious metal having a longer useful life than has heretofore been associated with silver contacts. It is a further object of the present invention to provide an operating pair of precious metal contacts in particular association with each other which shall have, throughout their useful life, a high degree of reliability of operation, substantially free from welding or sticking deformation and metal transfer. Other objects and advantages of the present invention will appear in the description hereinafter following and the drawing forming a part hereof in which the figure illustrates a side view of a pair of cooperating electrical contacts according to the present invention.

The invention deals with a contact assembly comprising at least a pair of cooperating precious metal contacts of which one contact element comprises essentially a palladium alloy containing from 90% to 99% palladium and from 1% to 10% ruthenium, and preferably 95.5%

'nited States Patent palladium with 4.5 ruthenium. The other contact element comprises from to 99.5% silver and from 0.5% to 10% palladium, and preferably 97% silver with 3% palladium.

In operating arrangement wherein the making and breaking of electrical current is accomplished by a pair of cooperating contacts, one of said contacts being a cathode and the other an anode, or one being a positive member and the other a negative member. The drawing shows, for example, positive member 1 secured to arm 2 and negative member 3 secured to arm 4, the positive member 1 is preferably composed of the palladiumruthenium alloy and the negative member is composed of the silver-palladium alloy. Otherwise, the contacts may be reversed.

Comparative tests with conventional silver and silver alloy contacts and those of the alloys of the present invention were made on a conventional automotive voltage regulator operating with generator currents of 0.75 ampere to 1.4 amperes, and the conventional silver contacts failed because of sticking after continuous use at 432, 720, 672, 768, 792 and 1130 hours of use under the six indicated separate tests. In comparison, a pair of cooperating contact members according to this invention showed 1436, 1464, 1460 and 1560 hours of continuous use before sticking occurred.

Consequently, it is apparent that the particularly associated contacts of the present invention in a majority of instances were operative approximately twice as long as the conventional silver contacts.

What we claim is:

l. A contact assembly comprising at least a pair of cooperating electrical contact members of which the positive contact member consists of an alloy of from 90% to 99% palladium and 1% to 10% ruthenium, and the negative contact members consists of 90% to 99.5% silver and 0.5% to 10% palladium.

2. A contact assembly according to claim 1, wherein the positive contact member consists of 95.5% palladium with 4.5% ruthenium.

3. A contact assembly according to claim 1, wherein the negative contact member consists of 97% silver with 3% palladium.

4. A contact assembly comprising a pair of contact arms, a positive contact member on one of said arms and a negative contact member on the other of said arms, said contact members facing each other, said positive contact member consisting of an alloy of from 90% to 99% palladium and from 1% to 10% ruthenium, said negative contact member consisting of from 90% to 95.5% silver and 0.5% to 10% palladium.

References Cited in the file of this patent UNITED STATES PATENTS 2,151,905 Emmert Mar. 28, 1939 2,207,292 Hensel et al. July 9, 1940 2,300,286 Gwyn Oct. 27, 1942 2,379,641 Keitel July 3, 1945 2,400,003 Hensel et a1. May 7, 1946 

1. A CONTACT ASSEMBLY COMPRISING AT LEAST A PAIR OF COOPERATING ELECTRICAL CONTACT MEMBERS OF WHICH THE POSITIVE CONTACT MEMBER CONSISTS OF AN ALLOY OF FROM 90% TO 99% PALLSDIUM AND 1% TO 10% RUTHENIUM, AND THE NEGATIVE CONTACT MEMBERS CONSISTS OF 90% TO 99.5% SILVER AND 0.5% TO 10% PALLADIUM. 